Message from discussion Zmodem PD 65c02 Source

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From: David.Emp...@actrix.gen.nz (David Empson)
Newsgroups: comp.sys.apple2
Subject: Re: Zmodem PD 65c02 Source
Message-ID: <1991Jul31.142010.4834@actrix.gen.nz>
Date: 31 Jul 91 14:20:10 GMT
References: <1991Jul30.115721.5784@crash.cts.com>
Organization: Actrix Information Exchange, Wellington, New Zealand
Lines: 28
Comment-To: ta...@pro-odyssey.cts.com

In article <1991Jul30.115721.5...@crash.cts.com> ta...@pro-odyssey.cts.com (Joe Quilici) writes:
> In-Reply-To: message from shrin...@Apple.COM
> 
> I remember someone stating that Z-modem is impossible to do on an Apple //,
> mainly because it is a streaming protocol and the Apple can't directly
> write the incoming data to the HD; instead having to pause to write.

ZMODEM doesn't have to be used in 'streaming' mode.  There is an
initial handshake in which the sender and receiver decide how they
will talk to each other.  If the receiver can't handle streaming, it
can tell the sender to wait for an acknowledgement before sending the
next block.  Alternatively it could send a message saying 'hang on,
I've lost some data.  Can you please re-send from byte XXX'.

Streaming doesn't require writing incoming data directly to the hard
drive.  It only requires that incoming data is not lost while the hard
drive is being accessed (i.e. interrupts are not disabled for very
long) and that the hard drive can be written to faster than the data
is coming in.

This is usually the case, unless you are writing to a floppy disk...



-- 
David Empson

USENET: David.Emp...@bbs.actrix.gen.nz